title: Proposal of a new 18F-FDG PET/CT predictor of response in rectal cancer treated by neoadjuvant chemoradiation therapy and comparison with PERCIST criteria.
abstract: OBJECTIVE
  The aim of this study was to correlate PERCIST criteria and a new criterion developed in our center that we named PREDIST (PET Residual Disease in Solid Tumor) with tumor regression grade (TRG) classification of pathologic response to neoadjuvant chemoradiotherapy (CRT) in patients affected by rectal cancer.
  
  
  METHODS
  Seventy-three consecutive patients affected by locally advanced rectal cancer (LARC) were retrospectively included. FDG-PET/CT scans were performed at staging time and after the end of CRT (mean time 6.5 weeks). The analysis was performed by PERCIST criteria 1.0 and PREDIST criteria based on a new definition of residual disease. We split the TRG system into responders (TRG1-2) and nonresponders (TRG3-5). Pearson chi-square analysis by cross-tabulations was performed.
  
  
  RESULTS
  PREDIST classification was statistically predictive of TRG response (P = 0.004, sensitivity 81.8% and specificity 54.9%). On the contrary, PERCIST criteria was not statistically correlated to TRG (P = 0.128) caused by a very low specificity (9.8%).
  
  
  CONCLUSIONS
  FDG-PET/CT scan is an accurate tool to predict preoperatively the response to CRT in LARC patients. The novel proposed criterion (PREDIST) seems to be helpful to discriminate responder by nonresponder patients.
authors.affiliation: From the *Nuclear Medicine Department, PET Unit, †Medical Physics Department, and ‡Radiotherapy Department, Santa Maria della Misericordia Hospital, Rovigo, Italy; and §Department of Radiology, University of Southern California, Los Angeles, CA.
authors.forename: Anna Margherita
authors.initials: AM
authors.lastname: Maffione
authors.forename: Alice
authors.initials: A
authors.lastname: Ferretti
authors.forename: Sotirios
authors.initials: S
authors.lastname: Chondrogiannis
authors.forename: Lucia
authors.initials: L
authors.lastname: Rampin
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Marzola
authors.forename: Gaia
authors.initials: G
authors.lastname: Grassetto
authors.forename: Carlo
authors.initials: C
authors.lastname: Capirci
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Colletti
authors.forename: Domenico
authors.initials: D
authors.lastname: Rubello
mesh_terms: D059248:Chemoradiotherapy; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D020360:Neoadjuvant Therapy; D018365:Neoplasm, Residual / Q000000981:diagnostic imaging; D049268:Positron-Emission Tomography; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000628:therapy; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
chemical_list: D019788:Fluorodeoxyglucose F18